The specific aim of this proposal is to define new human teratocarcinoma tumor-associated fetal embryonic antigens (TAFEA) by investigating the recently found reactivity of human alloantisera with human teratocarcinoma cell (TC) lines. The basic hypothesis to be investigated is that undifferentiated stem cells in human teratocarcinoma express fetal or embryonic differentiation antigens possibly controlled by a genetic region linked to HLA and that some of these antigens can be identified by antibodies found within HLA alloantisera. Other preselected sera will also be investigated including sera from patients with testicular cancer, sera from men following vasectomy, sera from women drawn sequentially through pregnancy, sera from individuals with a transfusion history, and sera from pregnant women subsequentially found to have a developmentally abnormal fetus. The elucidation of such determinants and/or the genetic region which controls them may add important insight into the growth regulatory mechanisms, genetic causes, and immune control of human teratocarcinoma; in addition, such information may help identify differentiation products representative of early histocompatibility precursor moieties similar to those controlled by the mouse T/t complex. In general, the basic experimental framework will screen and investigate the reactivity of several hundred human alloantisera with five human teratocarcinoma cell lines.